- Aortic valve area calculation
Aortic valve area calculation is an indirect method of determining the area of the
aortic valve. The calculated aortic valve orifice area is currently one of the measures for evaluating the severity of aortic stenosis. A valve area of less than 0.8 cm² is considered to be severe aortic stenosis. [cite journal | author = Charlson E, Legedza A, Hamel M | title = Decision-making and outcomes in severe symptomatic aortic stenosis. | journal = J Heart Valve Dis | volume = 15 | issue = 3 | pages = 312–21 | year = 2006 | pmid = 16784066] [cite journal | author = | title = Survival in elderly patients with severe aortic stenosis is dramatically improved by aortic valve replacement: results from a cohort of 277 patients aged >/=80 years. | journal = Eur J Cardiothorac Surg | volume = | issue = | pages = | year = | pmid = 16950629]
There are many ways to calculate the valve area of aortic stenosis. The most commonly used methods involve measurements taken during
echocardiography. For interpretation of these values, the area is generally divided by the body surface area, to arrive at the patient's optimal aortic valve orifice area.
Planimetry is the tracing out of the opening of the aortic valve in a still image obtained during echocardiographic acquisition during ventricular systole, when the valve is supposed to be open. While this method directly measures the valve area, the image may be difficult to obtain due to artifacts during echocardiography, and the measurements are dependent on the technician who has to manually trace the perimeter of the open aortic valve. Because of these reasons, planimetry of aortic valve is not routinely performed.
The continuity equation
The continuity equation states that the flow in one area must equal the flow in a second area if there are no shunts in between the two areas. In practical terms, the flow from the left ventricular outflow tract (LVOT) is compared to the flow at the level of the aortic valve. Using Echocardiography, the aortic valve area calculated using the time velocity integral (TVI) is most accurate method and is the preferred method. The flow through the LVOT, or LV Stroke Volume (cm3 or cc), can be calculated by measuring the LVOT diameter (cm), squaring that value, multiplying the value by 0.78540 giving cross sectional area of the LVOT (cm2)and multiplying that value by the LVOT TVI (cm), measured on the spectral Doppler display using pulsed-wave Doppler. From these, it is easy to calculate the area (cm2) of the aortic valve by simply dividing the LV Stroke Volume (cm3) by the AV TVI (cm) measured on the spectral Doppler display using continuous-wave Doppler.
Real-time three-dimensional echocardiography
Aortic valve replacement
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